Because Middle School is this weird transitional phase between Elementary and High School that no one liked or even remembered.
It's bad enough that so much crap is set in high school, we don't need the genre even more crowded.

@,
My only problem with your post is this:
It states here that you should have no knowledge of them:
Why not replace Ponssia and Shetland with the Dominion and Equestria? I imagine Equestria would be disgusted by your practices, and I'll leave it up to you whether the Flock is prejudiced against changelings.

@@EquestrianScholar,
I would expect that we wouldn't follow canon that much, since one would expect more nations to come in contact with each other if they existed, and retroactively including each and every player nation into MLP's history would take a while.
This freedom gives us license to get creative with the setting. For example, changelings (according to the comics) were born from a carnivorous plant. This would be difficult to explain within my own headcanon for changelings, and if I had to accept the comic's canon, the Dominion likely wouldn't be possible.
It also means we can do whatever we want for a map, so long as there's a consensus.
I'll drop their population numbers however.

The only problem I have with that conclusion is canon runs under the assumption that the Chrysalis Hive is one of the few, if not the only, changeling nation in existence. For a nation of the Dominion's size and population, it'd be absolutely impossible to conceal their existence. Not only would it be difficult to hide while actively trading, but the Dominion has had control over a population of ponies since the Discordian Era. Even if trading was conducted through these ponies, it'd be impossible to keep a secret such as this for long at all. Also, secrecy makes the Dominion virtually impossible as a nation. Gaining the food necessary to maintain such a large population would be nigh impossible if done completely in secret. This was one of the core ideas behind its creation: in contrast to Chrysalis, who believes secrecy and totalitarian control are the key to changeling survival, the Dominion and its Hives believe in cooperation and consensual feeding. This is due to several factors: 1) Their populations are too big to be supported by infiltrators only, 2) Food trading has led to economic growth and prosperity, 3) Facades are difficult to maintain and consume a lot of a ling's time, and are impossible to maintain en masse. Someone will notice when entire populations are fatigued by loss of emotion.

The way I see it, changelings can feed off of any emotion. Love might be the most nutritious and pleasing, but I'm sure negative emotions such as hate can also be consumed. These sorts of emotions would be alarming, since it means whatever they're feeding off of might be a threat to them. Negative emotions would probably taste bad for non-changelings as well.
Also, could we get a map? It'd be nice to have a visual representation of our positions.

Here, have a thing.
*Note, this section is yet to be confirmed. I'll be throwing EquestrianScholar a PM to see if this is acceptable, but because of how closely tied I felt the changelings should be with ponies, it wouldn't make sense for them to not have previous relations.
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Name: Scynthrae (Sky-nth-ray) Dominion
Goverment Type: Imperial, hegemonic, absolute monarchy - The government of the Dominion, in its most basic form, is an absolute monarchy. The Emperor is the ultimate authority, and the head of both the executive and legislative. However, there are two councils which work with the Emperor. The first of these councils is the Council proper, consisting of the Emperor, a group of advisors hand-picked by the Emperor, heads of state ministries, and a representative of the armed forces. The Council works directly with the Emperor to help coordinate and advise his reign.
The Scynthraen League, however, is made up of representatives from each hive under Dominion rule. Though these rulers have little actual power beyond their hives, the Dominion relies upon goodwill between them. Its namesake is ceremonial, respecting the origins of the Scynthrae Dominion as an alliance between hives.
Economic Model: State Interventionist, Dirigisme – Dominion economics are dominated by cooperative enterprises between workers, resulting in a large private sector. To ensure effective output and that certain corporate practices are emphasized, the state combines selective investment with regulation to bolster the economy and guide its economy. The state also has direct control of certain sections of industry.
Leader: Emperor Eukleides Kyrillos the Fourth
Category: Rational
Enviroment: Exists near the edge of the temperate zone, bordering the tropics. Controls large swaths of plains, however is centralized mainly in a large swamp and peninsula, which surrounds the west side of the plains, and forms their water border. Controls a portion of jungle to its southeast, and badlands to its northeast.
Two Abundant Resources:
Crops - as traditional food provides little nourishment to changelings, agriculture is obsolete. However, prolonged contact with ponies and other species have made it a lucrative business.
Luxury Goods - Changeling secretions (see: bee regurgitation) have properties that give it extraordinary flexibility. Using magic, it can change from a course liquid to a solid as hard as diamond. When mixed with emotions for long-term food storage, they are equivalent to flavored honey for non-changelings. Its various forms are in high demand among the other species as such, with the Dominion being the leading exporter.
Two Scarce Resources:
Food - as a predatory species, access to food is dependent on the economic situation, distance to prey, and several other factors. While the Dominion is well-entrenched globally, the political and economic climate of its trade partners are directly linked to food levels.
Precious Metals - changelings are historically isolationist, having little to do with the outside world. As this has only recently changed, precious metals have only just become important. They are far behind in their acquisition, and it is too early to say how rich their lands are.
Religion: Ekptotism - A view stemming from the philosopher Ekptotos' interpretation of changeling mythos, in Ekptotism it is believed all Changelings originated from Prothymia, the goddess of emotion, whom betrayed the pantheon of gods when she gave emotion, and therefore life, to all their creations. To punish her for her deeds, the pantheon banished her from the immortal plane, and created a race with which she was to govern. To further humiliate her, the gods stripped her and her children of emotion, instead forcing them to feed off it, or face death.
This has colored foreign relations for generations, leading to hotly contested issues. First and foremost is the problem of other races in general. Due to the variety of interpretations of Ekptotos and others' work, many Changeling societies deal with supremacism. Though less prevalent within Dominion society, it is still commonly believed that supremacists and xenophobics of other races are ungrateful of the gifts Prothymia has given them. Feeding is a controversial issue as well, as a result of whether feeding off other beings should be a consensual practice or not.
General Race Compostion: 15.7 million Changelings, 3 million ponies (1.4 million Earth Ponies, 1 million Pegasi, 0.6 million Unicorns), 1.4 million Griffons, 1 million Diamond Dogs, 0.1 million Dragons.
General Race Description: Changelings wear little to nothing at all, their exoskeletons serving as adequate protection from the elements. Ponies tend to only wear clothes in cold weather or during formal occasions, and diamond dogs normally wear vests, cargos, and backpacks for storing discovered items.
Two Primary Nation Traits:
Collectivist – The people of the Dominion put the collective before themselves, and as such are less prone to corruption, greed, or treachery. Patriotism is extremely common.
Adaptable – Dependent on another species for their own survival, changelings are naturally cunning creatures, able to not only create very convincing facades, but ingenious solutions and extraordinary shifts in mindset when faced with difficult problems.
Two Nation Values: Industrious, Cooperative
Culture and Description: A widespread myth about changeling society is that it's a hivemind, like that of an anthill or beehive. This is only slightly true – Changelings are as capable of free thought as any other sentient species, however there are social differences manifest from their evolutionary history. This takes the form of an inherently more collectivist and communitarian society: the individual is often overlooked in favor of the community as a whole. This is not to say the individual is ignored, but instead devalued. A changeling Hive is a collective of individuals – it requires social cohesion to run efficiently, and an inclination towards the community as a whole. Individuals are expected to value the Hive above their own needs, and to work cooperatively with others for the common good of the Hive. Dominion society is not entirely illiberal, however. Freedoms are respected as long as they are not destructive to the hive, creating a delicate balance between freethinkers and their hives. A repressed and unhappy individual is also unproductive and dangerous.
Buildings: Gigantic underground complexes called Hives remain the center of changeling life, housing all that's necessary for survival. Increasingly sprawling industrial sectors make up the land above alongside traditional aboveground residential sectors for ponies and some changelings. Farm communities are an unusual combination, with partially submerged villages serving as entrances to underground city halls and food repositories.
Foreign Policy: As the Dominion continues to grow in wealth and influence, it's become clear that its prosperity is a direct result of its cooperation with other species. This outlook has encouraged an era of diplomacy and trade, with an openness to other races similar to Equestria. However, it still maintains an expansionist trend, encouraging other Hives and communities to join it while searching for further lands to colonize.
History: Changelings are closely connected to the pony species – as a primary food source, their evolution was guided by their prey's abilities. As ponies grouped together, so did changelings. Hives are the manifestation of this trend. The Hive provided a steady stream of food, shelter, and protection, not only of its weaker members but of its territory. Unlike the ponies, however, the drive to outcompete prevented changelings from presenting a unified force. Instead, hives would rise and fall due to territory wars.
The Dominion began as the League of Scynthrae, an alliance between hives of the Scynthrae region. Pressured by the increased resistance from the now-united Equestria and other hives, the Kyndros Hive was able to unite several other hives under its command. Maintaining autonomy, hives benefited from Kyndros's military might in return for cooperation and resources. By this time, populations were becoming too large to maintain in secret, requiring bolder tactics.
This ceased upon Discord's rise to power. Once prosperous hives were almost exterminated by the mad dictator, entire armies routed by his might. Changelings returned to the underground, and afraid of Discord, hives began to wither. Angered and desperate, many began to look towards the League, their success luring many to its gates. This would prove to be the closest the changeling race would ever come to completely unifying.
Absorbing the League's hives and their armies, Kyrillos the Great declared a new Dominion, with Kyndros at its center, and began a campaign to consolidate what remained of its neighbors. Those who accepted – and many did – were peacefully assimilated, their hives provided food and protection. Resisters were squashed, their hives used to maintain their brethren. By the end of this crusade, the Dominion was not only in control of, but capable of retaining, a majority of the hives operating in or around Equestria, and a portion of Equestria itself.
*The rise of Celestia and Luna are typically seen as a turning point in foreign relations. Capable of defending itself against Discord, Kyrillos was visited by the alicorns in search of allies. Awed by their powers and interested in Discord's demise, the monarchs formed a pact. In return for better living conditions for its non-changeling inhabitants and supporting the usurping of Discord, the diarchs promised the Dominion that it would accept their current holdings, would maintain open trade, and reimburse lives lost and damage done during the war.
Changeling and non-changeling relations slowly improved during this time, long-term prosperity revealing the importance of cooperation. It was the Invasion of Canterlot that firmly entrenched this shift. As word traveled, ponies both in Equestria and the Dominion were outraged. Desiring to distance itself from Chrysalis and her Hive, the Dominion officially condemned the attack and began a campaign to improve Scynthrae-Equestria relations.
Quality of Life: The success of cooperation has led to astonishing leaps in rights for non-changeling species. While before they were viewed as prey, the Hives of the Dominion have begun to accept other races as their own. Its current economic growth also lends to lower unemployment rates, a shrinking lower class, and an increase in living standards. The Dominion's status as a welfare state along with the societal institutions of charity also contribute to low poverty levels.
Millitary Power: The Imperial Scynthrae Military, the descendant of what made the Dominion a reality. The military might of the Kyndros Hive was what gathered the various Hives of the Dominion under its rule, and with the dissolution of other Hive's militaries, it has become a force to be feared. It has not ceased its role as a political tool, however – rather, it could be said the Dominion has gone on to intimidating bigger, tougher opponents. There is no better example of the Dominion's brand of aggression than the Imperial Scynthrae Navy. Serving as a protector of her colonies abroad and the routes between them, the Navy's ability to reach parts of the globe nigh inaccessible by the army makes it the perfect political tool for a new age. In fact, the Dominion's use of this tactic has become a joke amongst the members of the Navy – if it earns the Emperor's attention, one should expect themselves on foreign shores within the week.
Even with a heavy emphasis on shows of force, the military is also highly effective at subversive tactics. The Dominion very rarely meets its enemies head-to-head on the battlefield, instead encouraging small skirmishes and covert actions followed by decisive engagements. Assassination, attacking supply lines, hit and runs, and harassment are all a part of the army's traditional modus operandi, however none are more effective than changelings' natural ability to disguise themselves. Through various means, changelings can infiltrate armies en masse, run reconnaissance unopposed, and lure opposing detachments into traps. Head-on engagements are more often clean up operations than traditional clashes, their opponents already dying from the inside out. For this purpose, foreign weapons and uniforms are stockpiled in accordance with which nations are the biggest threats, though these can be easily liberated from supply lines and fallen soldiers during war.
An equally important part of the Imperial military is compulsory conscription. Since the very beginnings of the Kyndros Hive, it has been considered a requirement for all members of society to undergo a few years of basic military training. Though it has its origins in defense in times of crisis, time has matured the concept into a rite of passage for citizenry. While technically under military jurisdiction, the Office for Civil Improvement focuses on reinforcing competence and proper conduct into its citizenry, and weeding out unproductive elements. This means that unless citizens are voluntarily transferred to a proper military branch, they aren't likely to be fit for combat. Under times of severe crisis, the Emperor can
Unnoticed by the larger world however is another tradition integral to not only the Dominion, but Changelings as a whole: Intelligence. Almost like a branch of the military, the Civil Intelligence Service has enjoyed a long history of use as a powerful political tool. From black operations, dedicated Infiltration missions, to simple surveillance, the CIS is often turned to when subtlety is a requirement outside the battlefield. Changelings' natural ability to disguise themselves makes it easy for the Dominion to insert agents into almost any nation imaginable, allowing for extensive spy networks to keep the Dominion updated on geopolitical situations.
Misc -
Capital City: The Kyndros (kine-d-rows) Hive
Motto: Eno̱ménoi tha epikratí̱sei. (United we prevail)
Various Symbols: Each hive has its own patron god, which serves as a shorthand for how the hives and their societies behave. Given the Kyndros Hive's position as the Dominion's capital its patron god, Artifex, the god of art and culture, is considered a state symbol. Prothymia's importance to Ekptotist philosophy, and the heart, a symbol of emotion and love, are also considered unofficial symbols for changelings and the Dominion. Each hive has a dominant carapace and eye color, and serve as the official color for that hive, as well as a way to identify one's heritage. Orange officially represents the Kyndros Hive and, due to its position as head of the Dominion, the color of the state. Black and green, the color of all changelings' exoskeletons and secretions respectively, are also predominant colors in flags and other symbolism, as they represent unity between changelings.

The problem isn't doing it, it's doing it enough to maintain a population. This process might be beneficial for a family, but the question is whether this can be scaled up enough to become an industry capable of supporting millions of people (ponies/dogs/lings/ et cetera).
This can be gained from other sources, and the amount of salt in sea water outweighs any benefits you'd gain otherwise.
I don't know much about Prussian history, but Russia is an excellent example of what not to do when running a nation. Sure, a military might be able to control an economy, but if they don't keep their populace happy, they could be dealing with insurgencies, riots, and revolution.

Since it appears that things are not only unlikely to change but temporary, I'll concede my argument in full.
I certainly hope this hasn't provoked any ill will between us, as I'd actually be interested in joining. I'm already in the process of filling out the form, I just need to cover a couple sections and it'll be finished. Could you perhaps give me some time to finalize things before we start?

The problem with the first two examples is that the technologically inferior armies typically fielded 10 times the troops, and even then faced heavy casualties to a much smaller force. European empires never fully mobilized their militaries due to logistics and appearances. Were we to see the kind of forces at play in the Napoleonic Wars, these uprisings would never have a chance. The nations in this roleplay might not be limited in that way, meaning scientific nations can bring to bear much larger forces. Traditional forces will either require gargantuan armies (a logistical nightmare) or incredible luck (very unlikely).
Then the nations have been poorly balanced. If a player has to take a majority of its time trying to win back its own nation due to inherent disadvantages, it's actively hampering the player's ability to freely enjoy their experience. Players should not be punished for playing a certain way, it's a game design no-no.
I suppose I could concede that point.
The problem is that through espionage, trade, and diplomacy, this pressure can be negated. Techniques and methods can be taught, machinery constructed, and with time stable production acquired. Likewise, powerful spells can be discovered, stolen, or taught, making them accessible (I hesitate to say easily). If a rational nation plays its cards right, it stands to out-compete all others through its open-mindedness. A bit OP, I'd think.
I'll give you Napoleon, but a lot of why the Nazi advance stalled was because they were fighting a two-front war. Germany very nearly had Russia, but Hitler was an idiot who didn't understand strategy (thank god). Had the Nazis taken care of the British before they took on the Soviets, it would have pounded it into submission before they could regroup.
As quadrupeds I imagine it'd be more than a little awkward riding on another horse. Non-magic users face considerable difficulty (realistically) in using weapons, add being on horseback and I'm sure it's a nightmare (moon).

I'm seeing a couple problems with this set-up that might make things problematic. Most importantly are the nation categories. While the magic vs. technology set-up allows less advanced nations to be competitive, you went a bit overboard. Magic might be capable of great feats, but I'd like to point you to the Battle of Omdurman between the British and Sudanese. Of the 52,000 warriors of Sudan, 10,000 were killed, 13,000 wounded, and 5,000 captured, compared to Britain's 8,200 Brits and 17,600 Egyptians and Sudanese, with only 47 dead and 382 wounded. Wikipedia itself quotes it as, "...a demonstration of the superiority of a highly disciplined army equipped with modern rifles, machine guns and artillery over a vastly larger force armed with older weapons..." And then there's the Battle of Blood River, where 464 Voortrekkers (Pioneers) and 200 servants killed 3,000+ of a 15,000-21,000 strong force of Zulus, with only three wounded, none killed.
My point is that, while Magically-inclined nations might be able to cope, traditional nations are obsolete, and would realistically be trampled by scientific nations. Rational nations would be capable of defending themselves, but the caps makes it very unlikely they'd succeed. There's also the problem that ideas and technologies are often traded. Magical and traditional nations might be justified in rejecting scientific discoveries, but there is absolutely no reason for why a rational nation would not integrate new ideas, as they wouldn't have reservations.
Also, the population restrictions are backwards. If we are to assume the industrial revolution is technological, and as such shunned by traditional nations, then they would need far bigger territories to even begin to match their scientific or rational counterparts' populations. Populations globally have skyrocketed since the industrial revolution, traditional nations would simply be incapable of the infrastructure necessary for supporting comparable populations.
I would suggest abolishing this system entirely, instead encouraging a spectrum, with technological on one end and magic on the other. Nations can either be entirely magical, entirely technological, have some inclination either way, or be perfectly balanced. This gives players more room to expand on the specifics behind why they use certain technologies and not others. As well, tech restrictions need to be lifted entirely, replaced by admin oversight. You don't have many players, so it'd be simple to maintain jurisdiction on what does and doesn't go without needless limitations on what can be done. Just point out a starting 'time period' for us to go on, and let things move forward from there.
At the very least, drop scientific nations' tech levels drastically, as otherwise they're going to completely dominate the other nations.
Uhm, a majority of MLP's races are quadrupeds. I don't think traditional cavalry is possible, or necessary. The closest thing to cavalry I can think of would be pegasi. The only races that might benefit from traditional cavalry are Diamond Dogs and Minotaurs.